1. Field of the Invention
The present invention relates to a camera system and, more particularly, to an external synchronization camera system using a composite synchronization signal containing a horizontal synchronization signal and a vertical synchronization signal provided as a system synchronization signal from an external source.
2. Description of the Related Art
In a monitoring camera system, usually, a slave camera is synchronized by using synchronization signals (a horizontal synchronization signal HD, a vertical synchronization signal VD, and a composite synchronization signal SYNC containing these signals) for a master camera. This is a well-known technique called xe2x80x9cexternal synchronizationxe2x80x9d. In this external synchronization, a process is performed for causing the phase of the synchronization signal of the slave camera to coincide with that of the synchronization signal of the master camera. At this time, ultimately, video signals are input from a plurality of cameras to one monitor.
However, depending on the location at which the slave camera is disposed, the time required for the synchronization signal of the master camera to reach each slave camera differs. If locked as it is, an out-of-synchronization video is produced on the monitor. For this reason, in each slave camera, adjustments are made so that out-of-synchronization does not occur on the monitor by phase-shifting a synchronization signal provided from the master camera so as to absorb out-of-synchronization portions which occur on the monitor.
When out-of-synchronization adjustments by this phase shift are made, two methods are available: a method in which a horizontal synchronization signal HD and a vertical synchronization signal VD are used as synchronization signals provided from the master camera, and a method in which a composite synchronization signal SYNC containing a horizontal synchronization signal HD and a vertical synchronization signal VD is used. FIG. 8 shows each waveform of the horizontal synchronization signal HD, the vertical synchronization signal VD, and the composite synchronization signal SYNC of the EIA (Electronic Industries Association) method (NTSC (National Television System Committee)-compatible black-and-white method). Generally speaking, the synchronization signal provided from the master camera is input to a timing controller IC within the slave camera. The construction of a camera system for each method is described below.
First, referring to FIG. 9, a description is given of a camera system using a horizontal synchronization signal HD and a vertical synchronization signal VD as synchronization signals provided from the master camera. In FIG. 9, an output signal of a CCD image pickup device 101 is input to a signal processing IC 102 whereby various signal processings are performed thereon, after which the signal is output as a video signal Video-OUT. A timing controller IC 103 generates a CCD driving signal for driving the CCD image pickup device 101, a signal processing driving signal for driving the signal processing IC 102, etc.
Here, the horizontal synchronization signal HD (master HD) and the vertical synchronization signal VD (master VD) provided from the master camera are input to the timing controller IC 103 after passing through an HD phase adjusting circuit 104 and a VD phase adjusting circuit 105. Then, the external vertical synchronization signal VD is provided to a V period counter 106, as a reset signal therefor, within the timing controller IC 103. The V period counter 106 counts up for each horizontal scanning period (1H) and generates an internal vertical synchronization signal VDxe2x80x2.
On the other hand, in a phase comparator 107 within the timing controller IC 103, the external horizontal synchronization signal HD is compared in phase at the rise edges with an internal horizontal synchronization signal HDxe2x80x2 which is generated by an internal HD generating circuit 108. This comparison result of the phase comparator 107 is provided to a PLL circuit 109. The PLL circuit 109 outputs a DC voltage corresponding to the comparison result of the phase comparator 107 and applies it across both ends of a variable-capacity diode 111 of a clock oscillator 110 which generates a clock 2MCK of a frequency twice as high as the master clock MCK which is a reference clock of this camera system.
In the camera system constructed as described above, phase shift for the external horizontal synchronization signal HD and the external vertical synchronization signal VD provided from the master camera is performed by the HD and VD phase adjusting circuits 104 and 105 before these signals are input to the timing controller IC 103. For the phase shift, generally, an analog monostable multivibrator having a simple circuit configuration is used.
This analog monostable multivibrator is capable of changing the phase of a signal by providing a fixed amount of a delay with respect to the fall or rise of the signal. Therefore, as is clear from the waveform chart of FIG. 8, phase adjustments can be performed on the horizontal synchronization signal HD and the vertical synchronization signal VD having a fixed period by the HD and VD phase adjusting circuits 104 and 105 using an analog monostable multivibrator, respectively.
Next, referring to FIG. 10, a description is given of a camera system using a composite synchronization signal SYNC as a synchronization signal provided from the master camera. In FIG. 10, an output signal of a CCD image pickup device 201 is input to a signal processing IC 202 whereby various signal processings are performed thereon and then the signal is output as a video signal Video-OUT. A timing controller IC 203 generates a CCD driving signal for driving the CCD image pickup device 201, a signal processing driving signal for driving the signal processing IC 202, etc.
Here, the composite synchronization signal SYNC (master SYNC signal) provided from the master camera is input to the timing controller IC 203, and the signal is separated into a horizontal synchronization signal HD and a vertical synchronization signal VD by a synchronization separation circuit 204 within the relevant IC 203. Then, the separated external vertical synchronization signal VD is provided to a V period counter 205, as a reset signal therefor, within the timing controller IC 203. The V period counter 205 counts up for each horizontal scanning period and generates an internal vertical synchronization signal VDxe2x80x2.
On the other hand, in a phase comparator 206, the separated external horizontal synchronization signal HD is compared in phase at the rise edges with an internal horizontal synchronization signal HDxe2x80x2 which is generated by an internal HD generating circuit 207. This comparison result of the phase comparator 206 is provided to a PLL circuit 208. The PLL circuit 208 outputs a DC voltage corresponding to the comparison result of the phase comparator 206 and applies it across both ends of a variable-capacity diode 210 of a clock oscillator 209 which generates a clock 2MCK of a frequency twice as high as the master clock MCK which is a reference clock of this camera system.
In a manner as described above, in the camera system of the former case using a composite synchronization signal SYNC as a synchronization signal provided from the master camera, as is clear from the waveform chart of FIG. 8, the composite synchronization signal SYNC has mixed synchronization signals of a 1H period and a 1/2H period, and the period of the composite synchronization signal SYNC is irregular; it is thereby impossible to directly perform phase adjustment on the composite synchronization signal SYNC by using an analog monostable multivibrator before the signal is input to the timing controller IC 203.
Therefore, when phase adjustment is required in this type of camera system, as shown in FIG. 11, it is necessary to separate the composite synchronization signal into the horizontal synchronization signal HD and the vertical synchronization signal VD by a synchronization separation circuit 211 once outside the timing controller IC 203, and to perform phase adjustment on the separated horizontal synchronization signal HD and the separated vertical synchronization signal VD by an HD phase adjusting circuit 212 and a VD phase adjusting circuit 213, and then to input them to the timing controller IC 203.
As a result, although, as shown in FIG. 10, the circuit scale can be remarkably reduced when the synchronization separation circuit 204 is formed inside the timing controller IC 203 than when it is formed outside, as shown in FIG. 11, the synchronization separation circuit 211 must be formed as an external circuit of an IC, and the phase adjusting circuits 212 and 213 are required, thereby causing the circuit scale to increase greatly and leading to increased cost.
The present invention has been achieved in view of the above-described problems. An object of the present invention is to provide a camera system which is capable of realizing phase adjustment for a composite synchronization signal SYNC by only adding a simple circuit in a case in which the composite synchronization signal SYNC is used as a synchronization signal provided from the master camera.
To achieve the above-mentioned object, according to one aspect of the present invention, there is provided a camera system comprising: a timing control circuit having a synchronization separation circuit which inputs the composite synchronization signal and which separates, from the composite synchronization signal, a horizontal synchronization signal and a vertical synchronization signal which are contained therein; and a horizontal phase adjusting circuit for adjusting the phase of the horizontal synchronization signal which is separated by the synchronization separation circuit and which is output from the timing control circuit, wherein the timing control circuit inputs the horizontal synchronization signal whose phase has been adjusted by the phase adjusting circuit, and generates an internal horizontal synchronization signal and an internal vertical synchronization signal in accordance with the horizontal synchronization signal after the phase adjustment and the vertical synchronization signal separated by the synchronization separation circuit.
According to another aspect of the present invention, there is provided an external synchronization system using a composite synchronization signal, which generates an internal horizontal synchronization signal and an internal vertical synchronization signal in accordance with a composite synchronization signal containing a horizontal synchronization signal and a vertical synchronization signal, the composite synchronization signal being provided from a master apparatus, and which operates a slave apparatus in accordance with the generated internal horizontal and vertical synchronization signals, wherein the slave apparatus comprises: a timing control circuit having a synchronization separation circuit for inputting the composite synchronization signal and for separating, from the composite synchronization signal, a horizontal synchronization signal and a vertical synchronization signal which are contained therein; and a horizontal phase adjusting circuit for adjusting the phase of the horizontal synchronization signal which is separated by the synchronization separation circuit and which is output from the timing control circuit, and the timing control circuit inputs a horizontal synchronization signal whose phase has been adjusted by the horizontal phase adjusting circuit and generates the internal horizontal synchronization signal and the internal vertical synchronization signal in accordance with the horizontal synchronization signal after the phase adjustment and the vertical synchronization signal separated by the synchronization separation circuit.
In the camera system constructed as described above, a composite synchronization signal provided from an external source is input to a timing control circuit, and the signal is separated into a horizontal synchronization signal and a vertical synchronization signal by a synchronization separation circuit inside the timing control circuit. Of the separated horizontal synchronization signal and the separated vertical synchronization signal, at least the horizontal synchronization signal is output once outside the timing control circuit and is phase-adjusted by a horizontal phase adjusting circuit, after which the signal is input again to the timing control circuit. Then, inside the timing control circuit, an internal horizontal synchronization signal and an internal vertical synchronization signal, which are references for the operation of this system, are generated in accordance with the phase-adjusted horizontal synchronization signal and the synchronization-separated vertical synchronization signal.
The above and further objects, aspects and novel features of the invention will become more apparent from the following detailed description when read in connection with the accompanying drawings.